Roger Zelazny in his sf novel Lord of Light conveys the distinction between fantasy and science during a comic dialog in Chapter One:

"Then the one called Raltariki is really a demon?" asked Tak.

"Yes—and no," said Yama. "If by 'demon' you mean a malefic, supernatural creature, possessed of great powers, life span, and the ability to temporarily assume virtually any shape—then the answer is no. This is the generally accepted definition, but it is untrue in one respect."

"Oh? And what may that be?"

"It is not a supernatural creature."

"But it is all those other things?"

"Yes."

"Then I fail to see what difference it makes whether it be supernatural or not—so long as it is malefic, possesses great powers and life span and has the ability to change its shape at will."

"Ah, but it makes a great deal of difference, you see. It is the difference between the unknown and the unknowable, between science and fantasy—it is a matter of essence. The four points of the compass be logic, knowledge, wisdom and the unknown. Some bow in that final direction. Others advance upon it. To bow before the one is to lose sight of the three. I may submit to the unknown, but never to the unknowable. The man who bows in that final direction is either a saint or a fool. I have no use for either."